A liquid crystal display (LCD), which is one of the most widely used flat panel displays, includes two plates having electrodes and a liquid crystal layer interposed between the plates. Voltages applied to the electrodes rearrange the liquid crystal molecules, thereby adjusting the transmitted amount of incident light. In various kinds of LCDs, a plurality of pixel electrodes are arranged in a matrix form at one of the two plates and a common electrode covers the entire surface of the other plate. The field generating electrodes may be formed by patterning a transparent conductive oxide layer made, for example, of indium oxide, indium tin oxide (ITO) or indium zinc oxide (IZO). When a transparent conductive oxide layer comprising ITO is annealed to crystallize the ITO and then patterned, an etchant containing strong acid such as ferric chloride or aqua regia is used. However, such an aqua regia based etchant may damage an underlying layer. Further, during a high-temperature process, a large amount of the etchant may be evaporated adversely altering the composition of the etchant and also contaminating the working environment.
Instead of annealing the transparent conductive oxide ITO layer to make it crystalline before patterning it to make a field electrode, an amorphous ITO coating may first be patterned using an etchant including oxalic acid and then annealed to form the field electrode. An oxalic acid based etchant offers high etching speed even at low temperature without damaging an underlying Cr, Al, or Mo layer. However, the oxalic acid based etchant is prepared by dissolving solid oxalic acid into water but oxalic acid has low water solubility and does not dissolve easily. As a result, oxalic acid deposits may be formed on pipes, nozzles, valves, or pumps, thus shortening the life span of a device or causing it to malfunction. Alternative etchants based on aqua regia or ferric chloride may be employed but these too may damage an underlying layer, sustain a change in the composition or contaminate the working environment.